This invention relates to a method of making a non-planar article such as an automotive heat shield from a preform made by roll bonding planar metal sheets.
In a roll bonding process, metal sheets are joined by the application of heat and pressure usually by hot rolling. It is normally understood that bonding only occurs in selected areas, the other areas being masked with a non-weld material which inhibits bonding. Articles which are commonly made by a conventional roll bonding process include evaporator panels used in refrigerators, radiators, air conditioners and freezers. Such articles are usually planar and will comprise a serpentine pattern of conduits for evaporator fluid formed during the roll bonding process by injecting a pressurized fluid, usually gas, between the sheets over said unbonded areas and thereby separating the sheets from each other in those areas.
Other applications of the roll bond process include the formation of multi-tube strips which may be bent over a mandrel subsequently to the application of pressurized fluid in order to define a parallel set of return conduits and thereby obviate the need for connecting spaced parallel tube strips with welded or brazed joints. It will be appreciated that such post fabrication steps made after roll bonding are of limited scope because of the danger of collapsing any of the conduits formed during the application of pressurized fluids and of kinking or piercing such conduits.
Another application of the roll bond process is to mask a major portion of the metal sheets with non-weld material and to place the roll bonded preform into a mould or cavity die so that upon injecting the pressurized fluid, the surfaces of the article will be formed by the shape of the die. Such a process is used for example in the fabrication of automotive gas tanks.
A problem to be addressed by this invention is the fabrication of more complex three dimensional or non-planar articles where bending over a mandrel or expanding into a die cavity are unsuitable. An example of such an application is an automotive heat shield provided to protect the occupants of a vehicle or sensitive electronic equipment from excessive heat produced by components of the exhaust system. Such shields have a relatively complicated structure formed to accomodate such heat emitting parts of a vehicle as for example a catalytic converter or an exhaust manifold.
It will be understood that in this application, an injecting fluid selected for its insulating properties is provided between the sheets of the shield. Other objects realized by the method according to this invention are more fully described with reference to a preferred embodiment described further below.